package com.srt.util;

import lombok.extern.slf4j.Slf4j;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CountDownLatch;

/**
 * @author rd06
 * @version 1.0
 * @date 2020-02-26 14:19
 */
@Slf4j
public class SnowIdUtil {
    /**
     * 私有的 静态内部类
     */
    private static class SnowFlake {


        /**
         * 内部类对象（单例模式）
         */
        private static final SnowFlake SNOW_FLAKE = new SnowFlake(1L, 1L);
//        private static final SnowIdUtil.SnowFlake SNOW_FLAKE = new SnowIdUtil.SnowFlake(1L, 1L);

        /**
         * 起始的时间戳，可以修改为服务第一次启动的时间
         * 一旦服务已经开始使用，起始时间戳就不应该改变
         * 2020-02-26 14:46:27
         */
        private final static long START_STMP = 1585027399L;

        /**
         * 每一部分占用的位数
         */
        private final static long SEQUENCE_BIT = 12; //序列号占用的位数
        private final static long MACHINE_BIT = 5;   //机器标识占用的位数
        private final static long DATACENTER_BIT = 5;//数据中心占用的位数

        /**
         * 每一部分的最大值
         */
        private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
        private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
        private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

        /**
         * 每一部分向左的位移
         */
        private final static long MACHINE_LEFT = SEQUENCE_BIT;
        private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
        private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

        private long datacenterId;  //数据中心
        private long machineId;     //机器标识
        private long sequence = 0L; //序列号
        private long lastStmp = -1L;//上一次时间戳


        /**
         * 通过单例模式来获取实例
         * 分布式部署服务时，数据节点标识和机器标识作为联合键必须唯一
         *
         * @param datacenterId 数据节点标识ID
         * @param machineId    机器标识ID
         */
        public SnowFlake(Long datacenterId, Long machineId) {
            if (datacenterId == null) {
                datacenterId = 1L;
            }
            if (machineId == null) {
                machineId = 1L;
            }
            if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
                throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
            }
            if (machineId > MAX_MACHINE_NUM || machineId < 0) {
                throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
            }
            this.datacenterId = datacenterId;
            this.machineId = machineId;
        }

        public static void main(String[] args) {
            for (int i = 0; i < 10; i++) {
                uniqueLong();
            }

        }

        /**
         * 产生下一个ID
         *
         * @return
         */
        public synchronized long nextId() {
            long currStmp = getNewstmp();
            if (currStmp < lastStmp) {
                throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
            }

            if (currStmp == lastStmp) {
                //相同毫秒内，序列号自增
                sequence = (sequence + 1) & MAX_SEQUENCE;
                //同一毫秒的序列数已经达到最大
                if (sequence == 0L) {
                    currStmp = getNextMill();
                }
            } else {
                //不同毫秒内，序列号置为0
                sequence = 0L;
            }

            lastStmp = currStmp;

            return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                    | datacenterId << DATACENTER_LEFT       //数据中心部分
                    | machineId << MACHINE_LEFT             //机器标识部分
                    | sequence;                             //序列号部分
        }

        private long getNextMill() {
            long mill = getNewstmp();
            while (mill <= lastStmp) {
                mill = getNewstmp();
            }
            return mill;
        }

        private long getNewstmp() {
            return System.currentTimeMillis() / 1000;
        }
    }

    /**
     * 获取long类型雪花ID
     */
    public static long uniqueLong() {
        return SnowFlake.SNOW_FLAKE.nextId();
    }

    /**
     * 获取String类型雪花ID
     */
    public static String uniqueLongHex() {
        return String.format("%016x", uniqueLong());
    }

    /**
     * 测试
     */
    public static void main(String[] args) throws InterruptedException {
        //计时开始时间
        long start = System.currentTimeMillis();
        //让100个线程同时进行
        final CountDownLatch latch = new CountDownLatch(5);
        //判断生成的20万条记录是否有重复记录
        final Map<Long, Integer> map = new ConcurrentHashMap();
        for (int i = 0; i < 5; i++) {
            //创建100个线程
            new Thread(() -> {
                for (int s = 0; s < 200; s++) {
                    long snowID = SnowIdUtil.uniqueLong();
                    log.info("生成雪花ID={}", snowID);
                    Integer put = map.put(snowID, 1);
                    if (put != null) {
                        throw new RuntimeException("主键重复");
                    }
                }
                latch.countDown();
            }).start();
        }
        //让上面100个线程执行结束后，在走下面输出信息
        latch.await();
        log.info("生成20万条雪花ID总用时={}", System.currentTimeMillis() - start);
    }
}
